Substantially Pb-Free Aluminum Alloy Composition

ABSTRACT

A substantially Pb-free aluminum alloy consisting essentially of (in weight percent) Si&lt;0.40; Fe&lt;0.70; Cu 5.0-6.0; Zn&lt;0.30; Bi 0.20-0.80; Sn 0.10-0.50 with the remainder being aluminum and incidental impurities. In one embodiment for applications that are sensitive to cracking from stresses generated during machining, the Bi/Sn ratio (in terms of weight percent) is less than 1.32/1 and producing in a T8 temper. On another embodiment for applications that are not sensitive to cracking from stresses during machining but would benefit from smaller machine chip size and more aggressive material removal rates, the aluminum alloy is produced using a T6 temper. The substantially Pb-free aluminum alloy has mechanical properties that include Ultimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength ≥38.0 KSI/262 MPa, and % Elongation ≥10%.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a substantially Pb-free aluminum alloycomposition, and method for making said alloy composition, whileachieving the machinability characteristics of their Pb-containingcounterparts.

2. Description of Related Art

Historically Pb-containing aluminum alloys such as 2011 and 6262(registered with the Aluminum Association in 1954 and 1960,respectively) have been used for demanding machinability applications.These applications require an alloy that can be machined at highmaterial removal rates while maintaining good machined surface finishesand producing machine chips that are small and easily removed from thework area to prevent jamming the machine tools. Aluminum alloyscontaining Pb met this need by providing intermetallic phases that actedas chip breakers in the material which enabled faster material removalrates, small machine chips and good machined surfaces. While Pb doesprovide an effective solution, it is a heavy metal and considered ahazardous material.

In an effort to reduce the adverse health effects and environmental riskthese alloys may pose, alternative Pb-free aluminum alloys capable ofsimilar machinability performance are desired. There have been severalattempts at developing free machining/Pb free alloys over the yearsincluding alloys 2012, 2111, 6020 and 6040. These alloys utilized Biand/or Sn as a substitute for Pb. While many of these alloys weresuccessful from a machining chip size and machined surface finishperspective, many producers of thin wall, complex parts found they couldnot achieve the material removal rates that were attained with Pbbearing incumbent alloys because the parts had a tendency to crack. Manyof these alloys were thus taken off the market or customers werecautioned to limit material removal rates for some applications. This isproblematic, considering many of the applications for the Pb bearingaluminum alloys are sold through distribution channels so the endmachining application was unknown to the material producer.

In an effort to avoid potential failures as a result of this cracktendency, the Pb-free alternative alloys that are still available areoften restricted in their availability and often have limits placed onthe machining parameters that do not achieve the same levels ofperformance as the Pb-containing alternatives. As a result there isstill a market need for a product that meets the machinabilitycharacteristics of the Pb-containing alloys, while also meeting thestrength requirements. Typically, for example, Pb-containing alloy2011-T3 has a minimum yield strength of 38 KSI/262 MPa.

BRIEF SUMMARY OF THE INVENTION

The substantially Pb-free aluminum alloy composition of the presentinvention provides a free machining product that achieves the same orsuperior machining performance in terms of high material removal rates,machining chip size and machined surface finish as their incumbentPb-containing predecessors.

The substantially Pb-free aluminum alloy composition of the presentinvention is not susceptible to cracking in thin wall, complex machiningunder severe material removal conditions. This is a critical distinctionthat has not been achieved in other inventions attempting to solve theafore-mentioned technical problem. Materials that are susceptible tosuch cracking conditions render the machining performance irrelevanteither by requiring substantially lower material removal rates ordisqualifying the material altogether to ensure the integrity of thefinal part.

The substantially Pb-free aluminum alloy composition of the presentinvention substantially meets or exceeds the material propertyrequirements of the current free machining materials. Specifically, in apreferred embodiment, the substantially Pb-free aluminum alloycomposition meets the minimum material properties for AA2011-T3including Ultimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength≥38.0 KSI/262 MPa, and % Elongation minimum >10%.

The substantially Pb-free aluminum alloy composition comprises, orconsists essentially of, the following components (in weight percent):Si<0.40; Fe<0.70; Cu 5.0-6.0; Zn<0.30; Bi 0.20-0.80; Sn 0.10-0.50 withthe remainder being aluminum and incidental impurities. In a preferredembodiment, the substantially Pb-free aluminum alloy compositionmaintains a Bi/Sn ratio of less than 1.32/1 (in terms of weight percent;1.32/1 being the eutectic ratio for Bi—Sn). In addition to this,producing the material in a T8 temper provides specific advantages formachining applications that are sensitive to machining cracks because oftheir high material removal rates and thin wall geometries. Conversely,specific machining applications that are not sensitive to machiningcracks because of more robust part geometries, but which would benefitfrom even higher material removal rates can be produced in a T6 temper.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will becomeapparent from the following detailed description of a preferredembodiment thereof, taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a schematic showing the operational process sequence for thesubstantially Pb-free aluminum alloy composition produced in the variousexamples in accordance with the present invention;

FIG. 2 is a conceptual drawing of the representative part used forevaluating machinability from a chip size perspective of a substantiallyPb-free aluminum alloy composition in accordance with the presentinvention;

FIG. 3 is a graph showing machinability for alloy/temper combinationsevaluated in Example 1, as measured in chips/gram;

FIG. 4 is a conceptual drawing of the machining crack susceptibilitytest part;

FIG. 5 shows pictures of observations made from the Machine CrackSusceptibility Test showing the four classifications used;

FIG. 6 is a graph showing Machining Crack Susceptibility Test resultsfor Example 1 as measured in % with no tears or blowouts;

FIG. 7 is a graph showing Machinability results for Example 2 asmeasured by chips/gram;

FIG. 8 is a graph showing Machining Crack Susceptibility Test resultsfor Example 2 as measured in % with no wrinkles, tears or blowouts;

FIG. 9 is a graph showing machinability results for Example 3 asmeasured by chips/gram;

FIG. 10 is a graph showing machinability results for Example 3 asmeasured by chips/gram for 2.000″ diameter rod; and

FIG. 11 is a Bi—Sn Phase Diagram.

DETAILED DESCRIPTION OF THE INVENTION

The substantially Pb-free aluminum alloy composition comprising, orconsists essentially of, the following components (in weight percent):Si<0.40; Fe<0.70; Cu 5.0-6.0; Zn<0.30; Bi 0.20-0.80; Sn 0.10-0.50 withthe remainder being aluminum and incidental impurities. In a preferredembodiment, Si, Fe, Cu, Zn, Bi, and Sn are the only componentsintentionally added to the alloy composition such that any othermaterial exist only as incidental impurities. Said incidental impuritiesare present in a total amount of less than 1 wt. %, or less than 0.5 wt.%, or less than 0.1 wt. %, or less than 0.05 wt. %. In one embodiment,the substantially Pb-free aluminum alloy composition maintains a Bi/Snratio of less than 1.32/1 (in terms of weight percent; 1.32 being theeutectic ratio for Bi—Sn).

Preferably, the substantially Pb-free aluminum alloy composition of thepresent invention substantially meets or exceeds the material propertyrequirements of the current free machining materials. Specifically, in apreferred embodiment, the substantially Pb-free aluminum alloycomposition meets the minimum material properties for AA2011-T3including Ultimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength≥38.0 KSI/262 MPa, and % Elongation minimum ≥10%.

Generally, the phrase “substantially Pb-free” is defined as having nointentional additions of Pb to the aluminum alloy composition as it isbeing produced. Preferably, any Pb that may be contained in the aluminumalloy composition is the result of tramp contamination. In a preferredembodiment, the aluminum alloy composition of the present inventioncontains<0.05 wt. % Pb. In another embodiment, the aluminum alloycomposition of the present invention contains<0.01 wt. % Pb. In anotherpreferred embodiment, the aluminum alloy composition of the presentinvention contains <0.005 wt. % Pb. In another preferred embodiment, thealuminum alloy composition of the present invention contains ≤0.003 wt.% Pb.

It is understood that the ranges identified above for the substantiallyPb-free aluminum alloy composition include the upper or lower limits forthe element selected and every numerical range and fraction providedwithin the range may be considered an upper or lower limit. For example,it is understood that within the range of Si<0.40, the upper or lowerlimit for Si may be selected from 0.30, 0.25, 0.20, 0.15, and 0.10 wt.%. In one embodiment, the amount of Si ranges from <0.20 wt. %. Inanother embodiment, the amount of Si ranges from <0.16 wt. %. In anotherembodiment, the amount of Si ranges from 0.10-0.16 wt. %. For example,it is also understood that within the range of Fe <0.70, the upper orlower limit for Fe may be selected from 0.60, 0.50, 0.40, 0.30, 0.20,and 0.10 wt. %. In one embodiment, the amount of Fe ranges from0.30-0.50 wt. %. In another embodiment, the amount of Fe ranges from0.33-0.44 wt. %. For example, it is also understood that within therange of Cu 5.0-6.0, the upper or lower limit for Cu may be selectedfrom 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, and 5.9. In one embodiment,the amount of Cu ranges from 5.1-5.8 wt. %. In another embodiment, theamount of Cu ranges from 5.13-5.63 wt. %. For example, it is alsounderstood that with the range of Zn <0.30, the upper or lower limit forZn may be selected from 0.20, 0.10, 0.05, 0.01, and 0.005 wt. % In oneembodiment, the amount of Zn ranges from 0.002-0.05. In anotherembodiment, the amount of Zn ranges from 0.002-0.044. For example, it isalso understood that within the range of Bi 0.20-0.80, the upper orlower limit for Bi may be selected from 0.30, 0.40, 0.50, 0.60, and0.70. In one embodiment, the amount of Bi ranges from 0.40-0.80. Inanother embodiment, the amount of Bi ranges from 0.20-0.40. For example,it is also understood that within the range of Sn 0.10-0.50, the upperor lower limit for Sn may be selected from 0.20, 0.30, and 0.40. In oneembodiment, the amount of Sn ranges from 0.20-0.50. Additionally, forexample, it is also understood that within the range of Bi/Sn ratio ofless than 1.32/1, the upper or lower limit for Bi/Sn ratio may beselected from 1.30/1, 1.25/1, 1.20/1, 1.15/1,1.10/1, 1.05/1, 1.00/1, and0.80/1. In one embodiment, the Bi/Sn ration may be between1.32/1-0.80/1. It is further understood that any and all permutations ofthe ranges identified above are included within the scope of the presentinvention. For example, the substantially Pb-free aluminum alloycomposition may consist essentially of the following components (inweight percent): Si<0.15; Fe<0.50; Cu 5.1-5.7; Zn<0.05; Bi 0.40-0.80; Sn0.20-0.50 with the remainder being aluminum and incidental impurities,while maintaining a Bi/Sn ratio of less than 1.32/1 (in terms of weightpercent; 1.32/1 being the eutectic ratio for Bi—Sn) or a Bi/Sn ratiofrom 1.32/1 to 0.80/1, having incidental impurities present in a totalamount of less than 1 wt. %, or less than 0.5 wt. %, or less than 0.1wt. %, or less than 0.05 wt. %.

In addition to this, producing the material in a T8 temper providesspecific advantages for machining applications that are sensitive tomachining cracks because of their high material removal rates and thinwall geometries. As such, a free machining, machining crack insensitivealuminum alloy may be produced. The aluminum alloy product has beenhomogenized to improve the recrystallization for improved grain sizecontrol. In a preferred embodiment, the alloy has a Bi/Sn ratio (inweight percent) of less than 1.32/1. In yet another preferredembodiment, the alloy has a Bi/Sn ratio (in weight percent) ranging from1.32/1 to 0.8/1. In yet another preferred embodiment, the alloy has aBi/Sn ratio (in weight percent) ranging from 1.20/1 to 1/1.

Conversely, specific machining applications that are not sensitive tomachining cracks because of more robust part geometries, but which wouldbenefit from even higher material removal rates can be produced in a T6temper. As such, a superior free machining aluminum alloy material forapplications that do not require machine crack insensitive propertiesmay be produced. The aluminum alloy product has been homogenized toimprove the recrystallization for improved grain size control. In apreferred embodiment, the alloy has a Bi/Sn ratio (in weight percent) isless than 1.32/1. In yet another preferred embodiment, the alloy has aBi/Sn ratio (in weight percent) ranging from 1.32/1 to 0.8/1. In yetanother preferred embodiment, the alloy has a Bi/Sn ratio (in weightpercent) ranging from 1.20/1 to 1/1.

It is important to note that the preferred process in accordance withthe present application does not include any naturally aging beyond thatwhich is inherent in the described processes disclosed herein.Specifically, the present invention does not include any T3 or T4naturally aging of the alloy composition.

Preferred processes for making the alloy composition of the presentinvention are similar to the processes described in U.S. Pat. No.5,776,269 and U.S. Pat. No. 5,916,385, the contents of which areexpressly incorporated herein by reference. In one embodiment, the alloyis initially cast into ingots and the ingots homogenized at atemperature ranging from about 900° to 1170° F. for at least 1 hour butgenerally not more than 24 hours, optionally followed either by fan orair cooling. In one embodiment, the ingot is soaked at about 1020° F.for about 4 hours and then cooled to room temperature. Next, in oneembodiment, the ingots are cut into shorter billets, heated to atemperature ranging from about 500° to 720° F. and then extruded into adesired shape. However, it should be understood that one of ordinaryskill in the art may select different times and temperatures and stillremain within the scope of the present invention.

In one embodiment, the extruded alloy shapes are then thermomechanicallytreated to obtain the desired mechanical and physical properties. Forexample, to obtain the mechanical and physical properties of a T8temper, solution heat treatment is conducted at a temperature rangingfrom about 930° to 1030° F., preferably at about 1000° F., for a timeperiod ranging from about 0.5 to 2 hours, water quenched to roomtemperature, cold worked, and artificial aged at a temperature rangingfrom about 250° to 400° F. for about 2 to 12 hours. However, it shouldbe understood that one of ordinary skill in the art may select differenttimes, quenching conditions, and temperatures and still remain withinthe scope of the present invention.

In one embodiment, to obtain the properties of a T6 of T6511 temper,prior to extrusion, the billets are homogenized at a temperature rangingfrom about 950° to 1050° F. and then extruded to a near desired size.The rod or bar is then straightened using any known straighteningoperation such as stress relieved stretching of about 1 to 3%. Tofurther improve its physical and mechanical properties, the alloy isheat treated by precipitation artificial age hardening. Generally, thismay be accomplished at a temperature ranging from about 250° to 400° F.for a time period from about 2 to 12 hours. However, it should beunderstood that one of ordinary skill in the art may select differenttimes, quenching conditions, and temperatures and still remain withinthe scope of the present invention.

The following examples illustrate various aspects of the invention andare not intended to limit the scope of the invention.

EXAMPLE 1

Billets were produced in 10 inch (254 mm) diameter with the targetcompositions found in Table 1. These billets were extruded and processedinto T3, T4, T6 and T8 tempers using the process parameters shown inFIG.1 to produce 1.000 inch (25.4 mm) diameter rod. Casting of thebillets was done using conventional direct chill casting techniques. The6040 alloy variants were produced in both press quenched (T6511 temper)and separate solution heat treatment (T651 temper) processes.Homogenization, extrusion, solution heat treatment, quenching, drawingand artificial aging operations were all completed using typicalindustry practices. Samples from this material were evaluated fortensile properties and machinability. The tensile property results areshown in Table 2. The mechanical property limits for 2011-T3 were usedas a minimum acceptable criteria. These results show that all butBISN-31-T451 materials pass the aluminum association minimum propertiesfor 2011-T3 (Yield Strength 38.0 KSI/262 MPa; Ultimate Strength 45.0KSI/311 MPa; 10% Elongation).

TABLE 1 Compositions for Example 1 (weight percent) Alloy Cast Si Fe CuMn Mg Zn Cr Pb Bi Sn Ti Zr B Ni BISN-01 0969 0.11 0.36 5.22 0.00 0.000.044 0.020 0.001 0.40 0.35 0.020 0.003 0.001 0.00 BISN-03 0971 0.110.38 5.32 0.00 0.00 0.003 0.000 0.002 0.49 0.27 0.025 0.002 0.001 0.00BISN-31 0973 0.12 0.42 5.40 0.00 0.00 0.004 0.000 0.002 0.63 0.49 0.0190.002 0.001 0.00 BISN-31 0975 0.12 0.39 5.47 0.00 0.00 0.003 0.000 0.0020.60 0.42 0.022 0.002 0.001 0.00 BISN-31 0977 0.11 0.40 5.40 0.00 0.000.003 0.000 0.002 0.60 0.42 0.021 0.002 0.001 0.00 BISN-04 0978 0.120.44 5.63 0.00 0.00 0.003 0.000 0.001 0.85 0.50 0.029 0.002 0.001 0.00BISN-06 0979 0.13 0.40 5.16 0.00 0.00 0.002 0.000 0.001 0.57 0.45 0.0240.002 0.000 0.00 2111-06 0981 0.12 0.35 5.37 0.00 0.00 0.003 0.000 0.0010.64 0.20 0.025 0.002 0.000 0.00 2111-31 0983 0.12 0.33 5.13 0.00 0.000.003 0.000 0.001 0.56 0.20 0.023 0.002 0.001 0.00 BISN-02 0985 0.130.39 5.34 0.00 0.00 0.009 0.002 0.001 0.67 0.60 0.015 0.002 0.001 0.00SNBI-CU 0986 0.11 0.36 4.36 0.00 0.00 0.003 0.000 0.001 0.59 0.41 0.0230.002 0.002 0.00 SNBI-NI 0989 0.13 0.40 5.24 0.00 0.00 0.003 0.000 0.0050.58 0.42 0.013 0.002 0.001 1.51 TEN6040 40-1 0.60 0.44 0.56 0.11 0.930.090 0.055 0.006 0.17 0.89 0.020 0.002 0.000 0.00 LAX6040 0445 0.720.29 0.43 0.07 0.95 0.170 0.078 0.025 0.29 0.85 0.036 0.000 0.000 0.00

TABLE 2 Mechanical Properties of Material Evaluated in Example 1 YieldUltimate % Lot Cast (KSI/ (KSI/ Elonga- ID # Alloy Temper MPa) MPa) tion299 969 BISN-01 T3 45.9/317 52.3/361 17.2 300 985 BISN-02 T3 46.1/31852.5/363 15.0 301 971 BISN-03 T3 45.3/313 51.5/355 16.5 302 978 BISN-04T3 46.3/319 52.6/363 15.3 303 975 BISN-31 T3 46.0/317 52.4/362 16.5 304973 BISN-31 T451 24.5/169 43.9/303 33.8 306 979 BISN-06 T3 44.5/30750.2/346 16.8 307 983 2111-31 T3 43.8/302 49.6/342 17.3 308 981 2111-06T3 45.5/314 51.4/355 15.8 310 989 BISN-NI T3 38.9/268 42.9/296 13.0 311986 BISN-CU T3 40.3/278 45.1/311 16.5 305 977 BISN-31 T8 42.1/29055.9/386 15.2 233 001 2011 T3 46.8/323 51.6/356 15.5 312 822 6040 T65144.6/308 49.3/340 18.5 000 000 6040 T6511 52.3/361 55.6/384 13.0

Machinability testing was conducted by producing a representative partthat utilizes several machining operations. This part is depictedconceptually in FIG. 2. Material removal rates were kept constantbetween materials by keeping the cutting speed and feed rate constantfor all machining operations. The chip size is evaluated by determiningthe number of clean, dry chips per gram. The results from thisevaluation are shown in FIG.3 and are compared with currentPb-containing free machining material, 2011-T3, as a benchmarkcomparison. This shows that the alloy/temper combinations tested werebetter or comparable to the incumbent material. Also tested in thismatrix were Pb-free 6040 compositions that are currently available inthe market. These have historically not performed as well as 2011-T3,and this test validated their inferior performance.

In order to test that the materials were not susceptible to cracking inthin wall, severe machining applications, a severe machining test wasdeveloped. This involves drilling out the center of the 1.000″ (25.4 mm)rod using 0.969″ (24.6 mm) diameter twist drill, resulting in a 0.015″(0.38 mm) wall thickness, as shown in FIG.4. The RPM and feed rate waskept constant at 1500 RPMs and 0.035″ (1.27 mm)/revolution feed rate.Once this test was completed, the specimens were examined for conditionsas depicted in FIG. 5. This test was developed for testing the materialssusceptibility to cracking under extreme machining conditions with thinwalls, high material removal rates and high torque applied. This testwas replicated a minimum of 12 times for each material tested that hadacceptable performance from a chip size and material propertyperspective. The percentage of parts with tears (or cracks) and blowoutswas recorded and the results are shown in FIG. 6. The BISN-31 isdesignated with the different tempers (T3, T4 and T8) in this figure forsimplification. This shows that the 2011 (incumbent Pb-containing alloy)consistently passed, as expected, as well as the Pb-free 6040 alloyvariants (note these alloy variants did not perform well from a chipsize perspective, however). The only experimental alloy that passed wasBISN-31-T4, but unfortunately this failed the tensile propertyrequirements.

Analysis of these results indicates that alloy/temper combinations withlower yield to ultimate strength ratios perform better from a machiningcrack susceptibility perspective. Closer analysis of BISN-01 throughBISN-04 compositions indicates that lower Bi+Sn content and lower Bi/Snratios are beneficial from a machining crack susceptibility perspectivewhen taking into account the severity of the failures. The Bi/Sn ratioappears to be the stronger influence relative to the composition relatedperformance input variables. This is illustrated in Table 3. Note thatthe Bi—Sn eutectic composition from a weight percent basis is at a ratioof 1.32 Bi/Sn (as shown in FIG. 11).

TABLE 3 Severity of Machining Crack Susceptibility Results for AlloysBISN-01 through BISN-04 Alloy Bi + Sn Bi/Sn % Wrinkled % Torn % BlowoutBISN-01 0.75 1.14 17% 77% 6% BISN-02 1.27 1.12 21% 50% 29% BISN-03 0.761.81 7% 13% 80% BISN-04 1.35 1.70 20% 20% 60%

EXAMPLE 2

Billets were cast in 10″ (254 mm) diameter and processed into 1″ (25.4mm) rod using the process depicted in FIG.1 and the compositions listedin Table 4. The % ROA (reduction of area) during the drawing operationwas evaluated in this study, particularly in the T3 temper. The effectof homogenization was also evaluated with cast 1110 being homogenizedand compared to the unhomogenized cast 1108. The 1″ (25.4 mm) rod wasevaluated for mechanical properties, machinability, and machining cracksusceptibility using the same techniques described in Example 1.

TABLE 4 Compositions and Tempers for Example 2 (weight percent) AlloyCast Bi Sn Cu Mg Fe Si Ni Mn Pb Cr Bi/Sn Bi + Sn Temper % ROA BI26 11020.27 0.24 5.31 0.00 0.42 0.15 0.00 0.00 0.00 0.00 1.13 0.51 T3 20.3 BI261103 0.28 0.23 5.40 0.00 0.35 0.13 0.00 0.00 0.00 0.08 1.22 0.51 T3 15.8BI26 1104 0.27 0.24 5.35 0.00 0.36 0.14 0.00 0.00 0.00 0.00 1.13 0.51 T39.3 BI26 1105 0.26 0.24 5.36 0.00 0.38 0.15 0.00 0.00 0.00 0.00 1.080.50 T8 15.8 BI26 1106 0.26 0.24 5.34 0.00 0.35 0.14 0.00 0.00 0.00 0.001.08 0.50 T651 17.4 BI39 1111 0.39 0.36 5.37 0.00 0.41 0.14 0.00 0.000.00 0.00 1.08 0.75 T3 20.3 BI39 1108 0.37 0.35 5.31 0.00 0.39 0.15 0.000.00 0.00 0.00 1.06 0.72 T3 15.8 BI39 1109 0.39 0.36 5.41 0.00 0.41 0.140.00 0.00 0.00 0.00 1.08 0.75 T3 9.3 BI39 1112 0.40 0.36 5.28 0.00 0.330.14 0.00 0.00 0.00 0.00 1.11 0.76 T8 15.8 BI39 1113 0.40 0.36 5.24 0.000.40 0.14 0.00 0.00 0.00 0.00 1.11 0.76 T651 17.4 BI39 1110 0.39 0.365.32 0.00 0.40 0.14 0.00 0.00 0.00 0.00 1.08 0.75 T3 15.8 BI39MG 11140.40 0.37 5.47 0.50 0.42 0.14 0.00 0.00 0.00 0.00 1.08 0.77 T451 17.4

The mechanical properties are shown in Table 5. This shows that all ofthe composition and temper combinations were capable of achieving theminimum 2011-T3 target mechanical properties (Yield Strength 38 KSI/262MPa; Ultimate Strength 45.0 KSI/311 MPa; 10% Elongation). The additionof Mg was successful in achieving these properties as well in the T4temper.

TABLE 5 Mechanical Properties of Material Evaluated in Example 2 YieldUltimate % Lot Cast % (KSI/ (KSI/ Elonga- ID # Alloy ROA Temper MPa)MPa) tion 338 1102 BI26 20.3 T3 45.3/313 50.5/348 15.0 341 1103 BI2615.8 T3 43.8/302 49.8/344 18.0 344 1104 BI26 9.3 T3 39.8/275 46.6/32218.0 345 1105 BI26 15.8 T8 39.2/270 53.8/371 15.0 347 1106 BI26 17.4T651 40.2/277 58.8/406 23.0 339 1111 BI39 20.3 T3 46.9/324 51.4/355 14.0342 1108 BI39 15.8 T3 43.8/302 49.7/343 18.5 343 1109 BI39 9.3 T338.4/265 47.1/325 12.0 346 1112 BI39 15.8 T8 39.2/270 53.9/372 14.0 3481113 BI39 17.4 T651 39.9/275 57.5/397 22.0 350 1110 BI39 15.8 T343.9/303 50.3/347 17.0 351 1114 BI39 17.4 T451 38.7/267 58.2/402 20.0

The machinability test, relative to chip size was evaluated with theresults depicted in FIG. 7. These results show that higher Bi+Sncompositions (BI39) perform better from a machinability perspective, asmeasured by chips/gram, and perform as good or better than the incumbent2011-T3. The lower Bi+Sn compositions (BI26) generally did not performas well as the incumbent 2011-T3, but were comparable. It also showsthat there is very little difference on the machinability as related topercent reduction area for T3 tempers, regardless of Bi+Sn levels. Theaddition of homogenization did not improve the machinability, butexamination of the grain structure revealed significant improvementrelative to peripheral coarse grain (recrystallized grain size on outerperiphery of the rod). Therefore the use of homogenization, while notnecessary for machinability, may be beneficial for some applicationsrequiring improved surface appearance (such as parts requiringanodizing). The T651 temper material, regardless of alloy composition,performed very well, with small chip size. The T8 tempers generallyperformed better than the T3 counterparts for a given alloy,particularly the BI26 composition.

In terms of the machining crack susceptibility test, these results areshown in FIG.8, in this case, wrinkles on the surface (per FIG.5) werealso considered unacceptable. These results show that while compositionBI26 performed significantly better than BI39 (confirming that higherBi+Sn makes the material more susceptible to machining cracks), thetemper has a much stronger influence. Note that all of the compositionsin this example had less than 1.32 Bi/Sn ratios. The T8 tempers did notcrack in this test regardless of composition, while the T6 samplesperformed very poorly. The T3 tempers all had some failures, with thehigher Bi+Sn containing materials having significantly higher failurerates. The BI26-T3 compositions had no failures in terms of tears orblow-outs per FIG.5, thus the Bi+Sn has a significant impact onperformance.

These results therefore demonstrate that by producing the material in aT8 temper, higher Bi+Sn levels can be utilized, thus achieving thesuperior machinability from a chip size perspective as well.

EXAMPLE 3

Billets were cast in 10″ (254 mm) diameter and processed into 1″ (25.4mm) and 2″ (50.8 mm) T3 and T8 rod using the process depicted in FIG. 1and the compositions listed in Table 6. The rods were evaluated formechanical properties, machinability, and machining crack susceptibilityusing the same techniques described in Example 1.

TABLE 6 Compositions and Tempers for Example 3 (weight percent) AlloyCast Si Fe Cu Mn Mg Zn Cr Pb Bi Sn Ti Bi + Sn Bi/Sn SN01 1172 0.16 0.455.76 0.03 0.00 0.00 0.00 0.002 0.25 0.21 0.009 0.46 1.21 SN01 1173 0.140.36 5.32 0.03 0.02 0.00 0.00 0.000 0.24 0.20 0.010 0.44 1.20 SN02 11750.15 0.39 5.55 0.03 0.00 0.01 0.00 0.002 0.35 0.21 0.013 0.56 1.65 SN021176 0.15 0.36 5.25 0.03 0.02 0.00 0.06 0.002 0.34 0.19 0.010 0.53 1.83SN03 1178 0.10 0.38 5.77 0.03 0.02 0.00 0.01 0.000 0.26 0.33 0.005 0.590.80 SN03 1182 0.16 0.39 5.37 0.03 0.01 0.00 0.01 0.003 0.24 0.30 0.0090.55 0.81 SN04 1180 0.15 0.36 5.35 0.03 0.02 0.00 0.00 0.002 0.35 0.350.006 0.70 1.00 SN04 1184 0.14 0.37 5.25 0.04 0.02 0.00 0.00 0.002 0.350.31 0.011 0.66 1.15

The mechanical properties are shown in Table 7. This shows that all ofthe composition and temper combinations were capable of achieving theminimum 2011-T3 target mechanical properties (Yield Strength 38 KSI/262MPa; Ultimate Strength 45.0 KSI/311 MPa; 10% Elongation).

TABLE 7 Mechanical Properties of Material Evaluated in Example 3Diameter Yield Ultimate % Alloy/ Lot (inch/ (KSI/ (KSI/ Elonga- TemperCast ID mm) MPa) MPa) tion SN01-T3 1172 402 1.000/25.4 45.0/311 50.4/34814.0 SN02-T3 1175 403 1.000/25.4 44.4/306 50.3/347 16.0 SN03-T3 1182 4041.000/25.4 44.5/307 50.7/350 15.0 SN04-T3 1184 405 1.000/25.4 43.9/30349.6/342 16.0 SN01-T8 1173 398 2.000/50.8 44.2/305 56.6/391 13.0 SN02-T81175 399 2.000/50.8 42.1/290 56.2/388 14.0 SN03-T8 1182 400 2.000/50.843.3/299 56.8/392 14.0 SN04-T8 1184 401 2.000/50.8 44.8/309 57.2/39514.0 SN01-T8 1172 760 1.000/25.4 42.7/295 55.8/385 14.0 SN02-T8 1176 7611.000/25.4 45.4/313 57.3/395 15.0 SN03-T8 1178 762 1.000/25.4 41.5/28655.3/382 15.0 SN04-T8 1180 763 1.000/25.4 42.8/295 55.0/380 15.0

The machinability test relative to chip size was evaluated with theresults depicted in FIG. 9 for the 1.000″ (25.4 mm) diameter material.The results show that the T8 performed superior to the Pb-containing2011 material, while the T3 material, which still performed acceptably,was not as good as the Pb-containing 2011 material. The test wasreplicated with the 2.000″ (50.8 mm) diameter to ensure the materialmachined well over a wider range of diameters. While the 2.000″ (50.8mm) diameter results were slightly worse than the Pb-containing 2011incumbent material in this test, it must be noted that from a chips pergram basis, it was better than any of the 1.000″ (25.4 mm) diameter testresults. Thus it can be concluded that the material performs wellthroughout these diameter ranges.

Machining crack susceptibility testing was also performed on the 1.000″(25.4 mm) diameter material considering wrinkles, tears and blow-outs(per FIG. 5) as failures. The results of this testing are shown in Table8.

TABLE 8 Summary of Results for the Machining Crack SusceptibilityTesting for 1.000″ (25.4 mm) Diameter Example 3 Percent Alloy TemperCast Lot ID Bi/Sn Passing SN01 T3 1172 402 1.21 5% SN02 T3 1176 403 1.830% SN03 T3 1178 404 0.80 0% SN04 T3 1180 405 1.00 0% SN01 T8 1172 7601.21 100% SN02 T8 1176 761 1.83 45% SN03 T8 1178 762 0.80 100% SN04 T81180 763 1.00 95%

These results confirm that for applications with severe material removalrates and part geometries with thin walls that are susceptible totearing, processing the material in a T8 temper and maintaining Bi/Snratios less than 1.32 virtually eliminates this failure mechanism.

Although the present invention has been disclosed in terms of apreferred embodiment, it will be understood that numerous additionalmodifications and variations could be made thereto without departingfrom the scope of the invention as defined by the following claims:

1. A substantially Pb-free aluminum alloy composition comprising thefollowing components (in weight percent of the aluminum alloycomposition): Pb 0-0.10; Si 0-0.40; Fe 0-0.70; Cu 5.0-6.0; Zn 0-0.30; Bi0.20-0.80; Sn 0.10-0.50; with the balance being aluminum save forincidental impurities; said alloy composition having a ratio by weightof Bi/l Sn of less than 1.32/1 said alloy composition manufactured usingonly a T8 or T6 temper to provide an alloy composition having anUltimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength ≥38.0KSI/262 MPa, and % Elongation minimum ≥10%.
 2. The composition of claim1 wherein said aluminum alloy composition has<0.05 wt. % Pb.
 3. Thecomposition of claim 1 wherein said aluminum alloy composition comprises0.10-0.16 wt. % Si.
 4. The composition of claim 1 wherein said aluminumalloy composition comprises 0.30-0.50 wt. % Fe.
 5. The composition ofclaim 1 wherein said aluminum alloy composition comprises 5.1-5.8 wt. %Cu.
 6. The composition of claim 1 wherein said aluminum alloycomposition comprises 0.002-0.05 wt. % Zn.
 7. The composition of claim 1wherein said aluminum alloy composition comprises 0.20-0.40 wt. % Bi. 8.The composition of claim 1 wherein said aluminum alloy compositioncomprises 0.20-0.50 wt. % Sn.
 9. The composition of claim 1 wherein saidaluminum alloy compositions comprising, optionally consisting of, thefollowing components (in percent (weight/weight) of the aluminum alloycomposition): Si 0-0.16; Fe 0-0.50; Cu 5.1-5.8; Zn 0-0.05; Bi 0.20-0.40;and Sn 0.20-0.50.
 10. The composition of claim 1 wherein said aluminumalloy composition has a ratio by weight of Bi/Sn in the range from1.32/1 to 0.8/1.
 11. The composition of claim 1 wherein said incidentalimpurities are present in a total amount of less than 0.5 wt. %.
 12. Thecomposition of claim 1, wherein said manufacturing includes only a T8temper.
 13. The composition of claim 1, wherein said aluminum alloycomposition is not subjected to a T3 or T4 temper.
 14. A method forforming an aluminum alloy comprising the steps: a. casting an alloybillet of the aluminum alloy composition of claim 1, b. optionallyhomogenizing the cast billet; c. extruding the cast billet to form anextrusion having a profile shape; d. solution heat treating theextrusion by heating to a soak temperature between 900-1060° F.(482-571° C.) and quenching from the soak temperature to roomtemperature; e. cold working the extrusion after step d) via drawing,stretching or rolling to a minimum of 5% reduction of cross sectionalarea; and f. artificial aging the extrusion of step e) to peak hardnessat a T8 or T6 temper to produce said aluminum alloy having an UltimateTensile Strength ≥45.0 KSI/311 MPa, Yield Strength ≥38.0 KSI/262 MPa,and % Elongation minimum ≥10%.
 15. The method of claim 14 wherein saidstep of homogenizing the cast billet occurs at a temperature within therange of 900-1050° F. for a time period of not less than 1 hour; andsaid step of solution heat treating the extrusion by heating to atemperature between 900-1060° F. (482-571° C.) occurs for 0.5 to 2hours.